The invention relates to a ram drilling tool for producing underground bores or for laying lines in the ground, for example at the same time as the production of a new underground bore or the widening of one which already exists.
Tools of this type are normally equipped for boring in a straight line or in curves, and then have an adjustable steering or boring head, for example one which can be rotated about its longitudinal axis in relation to the tool casing, whose angular position in relation to the tool casing determines the direction of motion of the tool.
The manner in which the relative position of the steering head and tool casing is adjusted, and how traveling on a curve is effected, can be very different. Examples of steerable ram drilling tools are found in U.S. Pat. Nos. 5,322,391, 5,350,254, 5,597,046, European patent 0 301 287 and in PCT published specification WO 94/05941, whose content is referred to expressly here.
In the tool according to the PCT published specification, the steering head is designed as a sphere, for example, and is mounted in the tool casing such that it can rotate; its axis of rotation extends at an angle in relation to the casing longitudinal axis. At the same time, the contact faces of the steering head and casing, which extend at right angles to the axis of rotation and are in contact with each other, likewise extend at an angle in relation to the casing longitudinal axis. This makes it possible to rotate the tool casing about its longitudinal axis while the ground holds the steering head firmly. As a result of such a rotation of the casing, the steering head can be moved into an eccentric position with respect to the tool casing, in which position travel on a curve takes place. The rotational angle between the steering head and the tool casing or, respectively, the two end positions of the steering head, are determined by a driver pin which is connected to the steering head and engages in a circular slot in the tool casing. If the pin rests on one end of the tool slot, then the steering head is in its position for traveling straight ahead (straight-ahead position), while, at the other end of the tool slot, it is located in the position for traveling on a curve (steering position). In this case, the tool is configured in such a way that the steering head is subject to a tendency always to move into one of the two working positions.
In order to bring the ram drilling tool from straight-ahead travel onto a specific curved path, the tool casing must be rotated with the aid of the compressed-air hose until the tool has reached the required angular position (initial position) for the desired curved path.
This rotational movement may be composed of two phases. In this case, the first phase consists firstly in only the tool casing being rotated until the driver pin has passed from the straight-ahead position into the steering position over the entire differential angle. As soon as this has taken place, the steering head and the tool casing are coupled to each other for the further rotational movement, that is to say the tool casing and the steering head rotate together until the initial position for traveling on a curve has been reached.
If, on the other hand, the driver pin is in its steering position from the start, then common rotation of the tool casing and of the steering head entails the simultaneous rotation of the hose. This case arises, for example, when the steering head unintentionally gets into the steering position during straight-ahead boring, and therefore a corrective movement of the tool casing is necessary, or when a correction to the direction is necessary while traveling on a curve.
Irrespective of the initial position for changing the direction of boring in the individual concrete case, in any case a change of direction requires rotation of the tool casing about its longitudinal axis, with the steering head stationary.
Such a rotation is possible only with the aid of the compressed-air hose connected to the rear end of the tool. However, this is associated with considerable problems, since the compressed-air hose must not be flexurally rigid and therefore cannot be torsionally rigid either. To this is added the fact that when the ram drilling tool is rotatedxe2x80x94even with the aid of a pipe linkage for the pressure-medium supplyxe2x80x94the ground friction acting on its casing has to be overcome. This friction can be very considerablexe2x80x94depending on the condition of the ground and on the external diameter and the length of the toolxe2x80x94so that during extended boring or in the case of rotation on a correspondingly long pressure-medium line (compressed-air hose) it is often even no longer possible to rotate the casing in the ground or to apply the forces necessary for this.
The friction between the casing and ground may certainly be avoided if the front part of the tool has a greater diameter than the rest of the casing. However, this breaks down because the friction between the casing and ground is imperative, in order that the ground can absorb the reaction forces directed counter to the boring direction.
In the case of the known tools with a compressed-air hose, a further disadvantage consists in the fact that because of the torsion of the compressed-air hose it is not possible to determine from outside the underground bore, at least not with the necessary accuracy, when the ram drilling tool begins to rotate, by which angle it actually rotates and at which angle the rotation has been completed.
However, since accurate boring is only possible when the steering head or an adjustable steering element assumes a predefined angular position in relation to the casing of the ram drilling tool, in practice it is critical in each case that the tool casing is rotated only for so long and to such an extent that the predefined steering angle is reached.
The invention is therefore based on the problem of providing a ram drilling tool having a steering head or steering element which is mounted such that it can rotate in the tool casing, said steering head or steering element permitting the most accurate possible rotation of the casing through a specific angular range or even by more than one complete revolution.
This problem finds its solution in a ram drilling tool having a steering element, for example a steering head, which is mounted in the tool casing such that it can move, for example rotate, and having a pressure-medium line, for example a compressed-air hose, which is connected to the tool casing such that it cannot rotate and whose casing is connected to a sleeve pipe such that it can rotate. The sleeve pipe is preferably connected to the tool casing such that it cannot be displaced axially.
This makes it possible to rotate the tool casing in relation to the steering element and the sleeve pipe with more or less ground friction, while the steering element is held firmly by the surrounding ground or with the aid of the sleeve pipe. The amount of ground friction which has to be overcome in the individual case essentially depends on the length of the sleeve pipe; the ground friction reduces with increasing length of the sleeve pipe and is dispensed with if the sleeve pipe extends from the steering element as far as the rear end of the casing.
In order to keep the friction low, a rotary bearing can be arranged between the sleeve pipe and the tool casing, preferably in the area of the steering element. A further rotary bearing can be located at the rear end of the tool.
Such a rotary bearing can comprise an inner ring in the sleeve pipe, for example having a rectangular cross section, engaging in a complementary recess in the tool casing. In this case, the inner ring can rest on one side on a shoulder on the tool casing and on the other side on the steering head or a transmitter casing which is arranged between the steering head and the tool casing but is connected to the tool casing such that it cannot rotate.
A further reduction in the frictional forces results if the free space between the sleeve pipe and the tool casing is sealed off from the outside, and therefore no soil can penetrate. Here, the free space can also be filled with a lubricant, for example with grease or oil.
In order to avoid inadvertent rotation of the casing in relation to the steering element, a releasable locking mechanism can be arranged between the sleeve pipe and the tool casing.
In any case, the sleeve pipe absorbs at least some of the ground friction and in this way ensures that the ram drilling tool can move forward in the ground under the influence of the percussion energy transferred to the casing from the percussion piston, which is moved to and fro pneumatically or hydraulically, and that, at the same time, rotation of the tool casing in relation to the steering head is possible without (excessively high) ground friction.